Woodrum: Swing planes and predicting GB-FB splits

From Bradley Woodrum at FanGraphs on August 30, 2012:

On July 18, 2009, Willy Aybar, who had not played in 6 days, who could barely play second base and had hardly proven himself as a hitter, got the start at second against eventual the AL Cy Young winner, Zack Greinke. Aybar went 4 for 4 with a game-deciding double.

Rays manager Joe Maddon told the media the choice to start Aybar had been a deliberate one, a decision based in the front office’s proprietary analysis. I remember the event — reading the post-game interview moreso than seeing the game — because it marked the first time in my baseball-viewing experience where I had seen a lineup decision apparently based according to ground ball and fly ball data.

Entering the 2009 season, Greinke had a 37.9% ground ball rate — making him one of the league’s more extreme fly ball starters (this has since changed). Aybar, meanwhile, finished his short career with a .349 wOBA against fly ball pitchers and a .300 wOBA against ground ball pitchers.

Since that July 18 game, the Rays have continued to be one of the very few teams to game the underappreciated GB-FB splits game. I suspect one of the main reasons for that is that teams — namely managers — cannot easily identify and predict the splits. Today, I would like to put forth a theory that suggests we can identify — with decent success — GB-FB splits after just watching a hitter take batting practice. Here is the theory:

THEORY: Batters with an uppercut swing will succeed more against ground ball pitchers, and hitters with a more level plane will succeed more against fly ball pitchers, and — naturally — hitters who can swing on both planes will have a smaller overall split.